Space Micropropulsion for Nanosatellites: Progress, Challenges and Future

Space Micropropulsion for Nanosatellites: Progress, Challenges and Future features the latest developments and progress, the challenges faced by different researchers, and insights on future micropropulsion systems. Nanosatellites, in particular cubesats, are an effective test bed for new technologies in outer space. However, most of the nanosatellites have no propulsion system, which subsequently limits their maneuverability in space.

• Explains why nanosatellite requirements need unique micro-technologies to help develop a compliant propulsion system
• Features an overview of nanosatellites and the global nanosatellite market
• Covers chemical and electric micropropulsion and the latest developments

• Language: English
• Publisher: Elsevier Science
• Release date: Mar 19, 2022
• ISBN: 9780128190388

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Section 1

Introduction

Outline

Chapter 1. Emerging of nanosatellites

Chapter 1: Emerging of nanosatellites

Kean How Cheah, PhD     Assistant Professor, School of Aerospace, Faculty of Science and Engineering, University of Nottingham Ningbo China, Ningbo, Zhejiang, China

Abstract

It has been more than 60 years since human sends the first artificial satellite into space. The space-related technologies have developed and evolved rapidly into a highly sophisticated and technically demanding regime. This chapter outlines the philosophy of small and microsatellites as a smaller, faster, cheaper and probably better alternative way for many developing countries to initiate their space program. In particular, the different aspects of CubeSat were examined and elaborated, from its conceptual inception in 1999, the first CubeSat launched in 2003, the way to put CubeSats into space, its development into capable means to carry out scientific and commercial missions, and even go beyond the Earth into Mars and Moon. The chapter ends with a highlight on the need for a micropropulsion system for CubeSat to fulfill its tremendous potential in the dawn of this new space.

Keywords

Constellation; COTS; Cubesats; Micropropulsion; Nanosatellites

1.1. Philosophy of micro- and nanosatellites

By the broadest definition, a satellite is a natural or artificial (man-made) body that orbits another body in outer space. For example, the moon is the natural satellite that is orbiting the Earth while the Earth is the natural satellite of the Sun. An artificial satellite (simply known as satellite thereafter) is a man-made object launched into space to orbit a predetermined body, for exampe, Earth, Moon, Mars as well as the Sun. Satellites are commonly categorized according to their physical size as shown in Table 1.1.

The first Earth-orbiting artificial satellite is the Soviet Union built Sputnik-1. It was sent into space on October 4, 1957, which marked the start of space exploration in human history [1]. Microsatellite has shown their existence at the very early stage of spaceflight. The Sputnik-1 is 83.6kg in mass (Fig. 1.1A), while the first US-built satellite that reached the orbit, the Explorer 1, has a mass of 14kg only (Fig. 1.1B) [2]. It is noteworthy that it was not the lack of technical know-how to build larger satellites but the less capability of launch vehicles of the time has limited the putting of larger satellites into space. As the capability of launch vehicles increased steadily, we have witnessed a shift in paradigm to bigger is better, as evidenced by the leap in satellite mass of Sputnik-2 to 508kg and Sputnik-3 to a whopping mass of 1327kg. As the space race between the United States and the Sovient Union intensified in the 1960s, the two space nations were competing to build larger, heavier, and more complex satellites and launch into space in the next 30 years.

Table 1.1

Figure 1.1  (A) Sputnik-1 with the radio transmitting antennas [1]; (B) Photo of William H. Pickering, James A. Van Allen, and Wernher von Braun (from left to right) carrying a full-scale model of the Explorer 1 satellite. Reprint with permission from F. McDonald, J.E. Naugle, Discovering Earth's radiation belts: remembering explorer 1 and 3, Eos, Trans. Am. Geophys. Union 89 (39) (2008) 361–363.

Such a trend was worrying the space community. The mission cost has since ballooned as a large aerospace organization or institution with a dedicated team of advanced technical expertise is required to not only design and develop, but also the subsequent management and operation of these sophisticated large satellites. The huge investment needed in a large satellite has practically limited the launch opportunity. For a large satellite with a complex mission, the development life-cycle could easily take more than 10 years as a series of comprehensive, stringent, and thus lengthy quality assurance and testing processes is necessary to ensure the reliability and robustness of the satellite before it is ready for launch. It was becoming a norm that compromised solutions were increasingly made to integrate diverse and incompatible functions into a large satellite platform [3] as flight opportunity is getting scarce. As a result, the compromised design could be poor and inefficient. The high mission cost coupled with the limited flight opportunity has provided room for conservatism to creep in. When any failure in a system could potentially ruin the entire costly mission, innovative and risky ideas are no longer preferable and encouraged.

Small satellites—Big future, title of 2010 Appleton Lecture by Prof. Sir Martin Sweeting at The Institute of Engineering and Technology on Jan 19, 2010

Realizing these demerits, micro- and nanosatellites have regained the attention of the space community. Functionalities of a large satellite could be distributed into several smaller satellites, which are less complex and economic to develop in a shorter period (Fig. 1.2) [4]. A malfunction in any smaller satellite in space can be readily replaced within a reasonable timeframe. Such smaller, faster, better, cheaper approach has provided NASA a cost-effective and therefore sustainable way in carrying out their future near-Earth scientific missions as well as interplanetary explorations. For example, NASA has planned to send at least a spacecraft to Mars during each Earth–Mars launch window opportunity in the future.

Figure 1.2  Comparison of traditional spacecraft and fractionated spacecraft. Reprint with permission from A. Poghosyan, A. Golkar, CubeSat evolution: analyzing CubeSat capabilities for conducting science missions, Prog. Aero. Sci. 88 (2017) 59–83.

Another key catalyst to the adoption of smaller satellite approach is the rapid advancement in microelectronics, in particular the microelectro-mechanical system technology. In 1965, Gordon Moore has first postulated the number of components in an integrated circuit to double every year in the coming decade (famously known as Moore's law). He then revisited the proposal in 1975 and revised the forecast to a sustained rate of increase (doubling every year) until 1980 before it is reduced to slower a rate of doubling every 2years [5]. Even with the reduced rate of increase, the pace of technological advancement in microelectronic is still considered fast if not rapid for the space industry. A large satellite mission that takes 10 years to complete would see its technological level in electronic systems obsolete by the time it is ready for launch. Such development in the consumer electronics industry has very positive motivation and influence for the space industry to reform from its traditionally cautious and rather slow pace mode of operation to one that is responsive and innovative.

A design-to-cost approach in developing a satellite, which imposes strict control over cost and schedule, was introduced at the third United Nations Conference on the Exploration and Peaceful Uses of Outer Space (UNISPACE III), Vienna, Austria in 1999. The approach was later pioneered by Surrey Satellite Technology Ltd. to contain the cost overrun, a persisting issue encountered in previous large satellite missions that adopted a design-to-capability approach [6]. The new approach encourages the utilization of up-to-date microelectronic technologies and is particularly suited for micro- and nanosatellites with relatively short mission lifetime, which translates into relatively less stringent requirements on the system components. After carefully screening and evaluation toward their susceptibility to the adverse effect of space environments, especially the highly energetic galactic rays and the trapped particles in the Van Allen radiation belt, the commercial-off-the-shelf (COTS) microelectronic components could be widely used in micro- and nanosatellites. This reduced the overall mission cost significantly without compromising the performance of the satellites in orbit. To date, COTS components with reasonably low cost, consumed less electrical power and spatial volume have proven capable to perform reliably in the low earth orbits [7].

Apart from the adoption of COTS components, another key factor to the resurgence of smaller satellite is the changing of management approach to one that draws inspiration from the IT industry management model, which employs small but responsive team to execute the project swiftly. This is in stark contrast to the conventional large aerospace organizations with a large number of staffs, layered management structures, and procedures. Specifically, the eleven (11) characteristics of such small and agile satellite teams have been outlined. Readers who would like to know more are encouraged to read the review on how modern small satellites change the economics of space [7]. The philosophy of micro- and nanosatellite becomes attractive for established space agencies as they now have more mission opportunities to demonstrate, test, and mature the novel technological ideas in space.

For the past few decades, space exploration has been dominated by the developed or relatively rich developing nations, such as the United States, China, Russia, countries of European Union, Japan, India, and Canada, primarily because of the high demands in advanced technological and economic resources to initiate a space program. The privilege to space has granted the people in those countries to enjoy better living, economic, and social standards, brought by the satellite technologies, such as weather forecast, communication, remote sensing, navigation as well as homeland security.

For developing and emerging countries, most of the resources are utilized for near-term and urgent needs, such as food, clean water, health care, education, and infrastructure. However, it is necessary to invest in human capitals, especially through strategic and advanced technological sectors, which is critical for the long-term development and prosperity of a country. To this end, micro- and nanosatellite program is particularly beneficial for these countries, by providing a unique and economically affordable pathway to expand their intellectual capitals [8] through scientific investigation and technological capacity building in the final frontier. The reduced mission complexity has allowed these countries to initiate their own space program, train their scientists and engineers to develop own communication, earth observation or defense security satellites, and eventually launch into orbit. Performance of their micro- and nanosatellites may not be comparable to those larger satellites but they have direct control and access to their satellites without relying on the major satellite service providers.

Although there are various benefits and advantages offered by micro- and nanosatellites as discussed previously, large satellites still have a unique role in the space industry and remain the preferred satellite form factor for certain applications. For example, GEO communication applications prefer huge and powerful satellites owing to their multiple payloads carrying capability to provide adequate bandwidth for the area of coverage.

1.2. The birth of CubeSats

After years of continuous development, the capability of micro- and nanosatellites has been steadily improving in terms of platform design, payload performance, and ground control management. Around the year 2000, these smaller satellites have accumulated sufficient capability and evolved from the early days of demonstration purpose into useful utility missions, in particular earth observation of commercial value [7]. Specifically, the improvement in attitude control, precise pointing, onboard data storage, and data downlink combined with the advance in imaging sensor technology has increased the resolution of images captured in low earth orbits. For instance, the three-axis stabilized TopSat, a 120kg satellite launched in 2005, was able to capture images with resolution down to 2.8 and 5.6m of ground sample distance for panchromatic and multispectral images, respectively. The captured images could be downlinked to a ground station within a few minutes using its X-band transponder at 11Mb/s [9].

While microsatellites (<100kg) have reduced the mission cost significantly, they are still considered capital intensive for educational purposes. Establishing a comprehensive educational training program, which covers all stages of satellite missions, that is, from design, manufacturing, assembly, testing, launch, and finally operate the satellite, is essential to provide valuable hands-on experiences in nurturing the existing students into competent scientists and engineers to meet the growing demand in the space industry.

Recognizing the need for science and engineering students to get involved in a real satellite mission from early on, the idea of employing much smaller satellites, between nano- and picosatellite class, was considered. In 1999, Jordi Puig-Suari (from California Polytechnic State University, Fig. 1.3A) and Bob Twiggs (from Stanford University, Fig. 1.3B) have collaborated and initiated a picosatellite project, which was supposed to launch on a Russian rocket [10]. However, the launch opportunity was canceled unexpectedly. This has prompted them to start thinking to transform the pico-class satellite into a standard to extend the reach of such tiny satellite among the academic communities. With a mass of less than 1kg, the physical size of a picosatellite is small. To harvest the maximum solar power and convert it into useful electricity, one needs to mount as many solar cells as possible on the surfaces of a picosatellite, such consideration leads to the setting of the picosatellite in a cube shape. The idea eventually evolved into a standardized pico-class satellite in a form factor of 10cm cube (which can hold 1kg of water), and thus known as CubeSat [11]. The inception of CubeSat has attracted tremendous interest from universities around the world, with almost all major universities have had their own CubeSat program. The rapid advances in the fields of microelectronics, telecommunications, materials, and instrumentations have accelerated the development of CubeSat-related technologies and reduced the cost further. Now, it is not just affordable for established and big universities, but smaller universities, even high school students could access space via a CubeSat program.

Figure 1.3  (A) Prof. Jordi Puig-Suari, who is holding a 1U CubeSat; (B) Prof. Bob Twiggs. Reprint with permission from R.A. Deepak, R.J. Twiggs, Thinking out of the box: space science beyond the CubeSat, J. Small Satell. 1 (1) (2012) 3–7.

CubeSats are classified as pico- to nanoclass of satellites, which were built according to a specific set of standards such as shape, size, and weight as outlined in the Cubesat design specifications (CDS). A standard one CubeSat unit (1U) is referring to a 10 × 10 × 10 cm cube with a mass of up to 2kg (an increase from 1.33kg, as stated in the latest CDS Rev. 14). Throughout the years of development, CubeSats have grown into larger sizes, such as 1.5, 2, 3, 6, and 12U (even size as large as 24U has been proposed) to meet the increasing demand of the mission on advanced functionality and capability of the satellites. Examples of the mechanical layout of a 1, 2, 3, and 6U CubeSat size are shown and compared in Fig. 1.4 [12].

Standardizing the specifications of the satellites offers multiple advantages. Smaller companies can develop individual CubeSat subsystems, mass-produce using COTS components, and supply to different CubeSat developers, who later stack and assemble the subsystems into a highly integrated CubeSat according to the mission requirements (Fig. 1.5) [13]. Such modular approach of satellite development permits batch-production, in which the economy of scale would reduce the overall cost, as witnessed in the consumer electronic products, such as PCs, smartphones, and other gadgets. The setting up of standards is also promoting the sharing and exchange of information among the CubeSat community as a common language has been widely used in communication. Since then, many CubeSat-related conferences, workshops, and exhibitions have been hosted by various organizations for the stakeholders to engage and interact. Furthermore, the standardized physical dimension of CubeSats facilitates the general transportation and deployment into space as a common set of procedures and systems could be used, independent of CubeSat developers.

Figure 1.4  Volume of a 1, 2, 3, and 6U CubeSat (start from left). Reprint with permission from P. Machuca, J.P. Sánchez, S. Greenland, Asteroid flyby opportunities using semi-autonomous CubeSats: mission design and science opportunities, Planet. Space Sci. 165 (2019) 179–193.

Figure 1.5  Modular design architecture allows integration of subsystems/components from different developers into a CubeSat. Reprint with permission from K. Schilling, Perspectives for miniaturized, distributed, networked cooperating systems for space exploration, Robot. Autonom. Syst. 90 (2017) 118–124.

1.3. Launching of CubeSats

For most of the rocket launches, there is usually some excess in launch capacity after integrating the primary satellite, allowing the possible inclusion of small secondary payloads. In the early days, most of the CubeSats were launched into orbit via such ridesharing launches as secondary payload (or called piggyback satellite), sharing the ride with a primary payload (Fig. 1.6). While the associated launching cost is low, it is subjected to requirements and restrictions imposed by the launch service provider and the primary satellite owner. For example, the piggyback satellite owner has no control over the launch date, and on some occasions, needs to deliver the satellite to the launch site for integration with the launch vehicle weeks before the actual launch date to accommodate the schedule of the primary satellite. In addition, the primary mission always determines the final altitude for orbit insertion. In most cases, the deployment of CubeSats is only carried out once the primary satellite has been separated from the launch vehicle, clearing the potential risk of in-orbit collision.

Figure 1.6  Piggyback satellites on H-IIA launch vehicle. Reprint with permission from JAXA; Rocket image: Courtesy of Mitsubishi Heavy Industries Ltd.

With the increasing demand in CubeSat launching, there are dedicated rideshare launches, where a combination of multiple small- and/or CubeSats are launched together. As of January 2021, SpaceX holds the record with 143 satellites of different sizes launched on a single rocket beating the previous record by Indian's PSLV C-37 launch of 103 satellites. Such mode of ridesharing offers the riding satellites more equal partnership, and a therefore fairer share of control over the final altitude (as opposed to the domination by the primary satellite), where deployments of satellites at multiple altitudes are possible, as long as it is within the capability of the launch vehicle. Although dedicated rideshare launches increase the launch opportunities for CubeSats, the managing of diverse requirements from different stakeholders, that is, launch service providers and satellite developers of each ridesharing satellite, as well as the logistic arrangement, is a challenging task [7]. Currently, NASA and ESA are coordinating and supporting the launch of CubeSats developed by universities, research institutions, and schools through the CubeSat Launch Initiative and Fly Your Satellite Program, respectively.

Since 2014, there is a new option to launch the CubeSats into orbit. The CubeSats could be sent as part of the cargo on a resupply mission to the International Space Station (ISS), where the CubeSats are launched into space using a dedicated deployer. JAXA has developed the first of this kind deployer, called the Japanese Experimental Module (JEM) Small Satellite Orbital Deployer (J-SSOD) to deploy the CubeSats, up to 6U in form factor, from the ISS [14].

In a typical deployment procedure, the CubeSats are preloaded into a dispenser, known as Satellite Install Case (each can hold up to 3 units of CubeSat), and launched as cargo to ISS. Once the cargo reaches the ISS, Satellite Install Cases are transferred into the Japanese KIBO module, where a crewmember (an astronaut) will load them onto J-SSOD, which is equipped with an electrical box and separation mechanism for deployment. The J-SSOD assembly (with a maximum of two Satellite Install Cases) is then attached to the multipurpose experiment platform (MPEP) and is slid out from the KIBO's airlock to the space environment. Subsequently, the KIBO's robotic arm Japanese Experiment Module Remote Manipulator System (JEMRMS) grasps the MPEP assembly and transfers it to the deployment point (Fig. 1.7A), which is usually in the direction opposing the travel direction of ISS and pointed to nadir-aft 45 degrees. In the final step, the spring on Satellite Install Case jettisons the CubeSats into space sequentially (Fig. 1.7B) [15]. The first J-SSOD deployment was successfully carried out on October 4, 2012, in a two-time deployment. In the first deployment, it was operated by JAXA astronaut Akihiko Hoshide on orbit to release the first two CubeSats (WE WISH and RAIKO). This was followed by the second deployment operated by the mission control on the ground to release the remaining three CubeSats (FITSAT-1, F-1, and TechEdSat). Soon after the successful deployments of CubeSats from ISS, NanoRacks LLC (based in Houston, US) has developed the first commercial deployer, sharing the same facilities and deployment procedures with J-SSOD. The Nanoracks CubeSat Deployer (NRCSD) can hold up to 6 units of CubeSats while the upgraded NRCSD DoubleWide has doubled the capacity to 12 units of CubeSats.

On a very rare occasion, the Peruvian Chasqui 1 cubesat was launched by a Russian cosmonaut by tossing the tiny satellite from ISS by hand during a spacewalk in 2014.

Figure 1.7  (A) Location of JEMRMS and JEM Airlock in KIBO lab; (B) Deployment of CubeSats. Reprint with permission from Y. Nogawa, S. Imai, 24 - Launch from the ISS, in: C. Cappelletti, S. Battistini, B.K. Malphrus (Eds.), Cubesat Handbook, 2021, Academic Press, pp. 445–454.

1.4. First CubeSats

The first group of CubeSats was launched on June 30, 2003, with a Rokot rocket from Plesetsk, Russia. The mission has put six CubeSats into a sun-synchronous orbit: the Danish AAU CubeSat and DTUSat, the Canadian CanX-1, the US QuakeSat, and the Japanese XI-IV and CUTE-1.

AAU CubeSat was built by students from Aalborg University, Denmark. The students had initially intended to conduct an earth observation mission but later found challenging to execute in a 1U CubeSat [16]. It was then decided that the CubeSat would carry a CMOS camera of 1.3 megapixels in 24-bit colors with a resolution of 150×120m and used this opportunity as a technology evaluation preparing for future missions in CubeSat platform. Unfortunately, the mission was short-lived, and it lasted for about two and a half months before the battery lost all its capacity with only basic beacon data signal received on the ground. Postanalysis has suggested that the transmitted signal was too weak to establish an effective data link for communication and download of housekeeping